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I've recently noticed what sounds to be a the noise of a flap or valve shutting a few seconds after the engine shuts down. Not too concerned, but it sounds like it could do with some lubrication whatever and wherever it is. Anybody got any ideas?

Ok, I made sure that the vent fan was off when I turned off the ignition and there was no sound of a flap closing. Instead there was a high pitched electrical whine which went on for about five minutes. Then the clunk of a relay or solenoid closing and the whine stopped. Any idea what that's all about?

Sorry, It's a 2003 Z4 with 57,000 Kms (35,450 miles) on the clock. The noise was certainly there for a while. I had got out of the car and had almost walked out of the garage, came back, tried to locate the noise - car or household - then opened the hood. But as I did so it stopped. I know it wasn't the fan.
I'll see if it happens again today. Great car, but too many electronic gadgets for my liking

Too many electronic gadgets??? This is Fred Flintstones car compared to 99% of all the others out there.

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.How does something immoral, when done privately, become moral when it is done collectively?
Furthermore, does legality establish morality?
Slavery was legal; apartheid was legal; Stalinist, Nazi, and Maoist purges were legal. Clearly, the fact of legality does not justify these crimes. Legality, alone, cannot be the talisman of morel people. - Walter E. Williams

I am Fred Flintstone and I stopped playing with avionics back in the early 70's. I have only just graduated from a 1971 MGB where I knew what every squeak, rattle and thump was and could and did fix it myself. Anyway, whatever it was didn't happen this morning and I know a cooling fan when I hear one. So maybe it's one of those intermittent faults, or it will never come back.

Actually, since you are well versed in British Electrics and you know it not a mechanical issue, you should be right at home. Probably a sticky relay. Which one? Who knows?

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.How does something immoral, when done privately, become moral when it is done collectively?
Furthermore, does legality establish morality?
Slavery was legal; apartheid was legal; Stalinist, Nazi, and Maoist purges were legal. Clearly, the fact of legality does not justify these crimes. Legality, alone, cannot be the talisman of morel people. - Walter E. Williams

If you all think its a valve of some type, you could disconnect the electrical connector on the DISA valve, then shut down the engine and listen...

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.How does something immoral, when done privately, become moral when it is done collectively?
Furthermore, does legality establish morality?
Slavery was legal; apartheid was legal; Stalinist, Nazi, and Maoist purges were legal. Clearly, the fact of legality does not justify these crimes. Legality, alone, cannot be the talisman of morel people. - Walter E. Williams

I have had the same issue on occasion. When I turn off the engine you can hear an electrical hum sound, it is not the fan, I checked. It does not happen very often. It usually stops after awhile. One time the hum started, I went inside the house and a few minutes later came back out and it was still humming. I started up the engine and when I turned the engine off the hum was gone. I have no idea what is causing this ??

Is it coming from the back? Both my X3 and Z4 do this and it is some kind of fuel vapor something. It reclaims the fuel or something so that it is not released into the environment, or something like that...I know it is normal just not 100% sure why :-)